In an imaging device using a solid-state image sensing device such as a CCD or CMOS image sensing device, which is mounted on a digital still camera and the like, an optical filter (near-infrared cut filter) that transmits visible light and blocks near-infrared light has been used in order to favorably reproduce a color tone and obtain a clear image. In order to obtain favorable color tone reproducibility, in particular, in such an optical filter, the optical filter is required to make visible light transmit, and to exhibit a spectral transmittance curve in which ultraviolet light and near-infrared light are cut-off. As such an optical filter, there has been conventionally known an optical filter including an absorption layer (a light absorption layer) containing a near-infrared absorbing dye, and a reflection layer (a light reflection layer) formed of a dielectric multilayered film which cuts-off light in an ultraviolet wavelength region and an infrared wavelength region. In this optical filter, a spectral transmittance curve of the dielectric multilayered film itself changes (shifts) depending on an angle of incident light. For this reason, the optical filter as above tries to obtain a spectral transmittance curve excellent in color reproducibility by overlapping an absorption wavelength region of the absorption layer which contains the near-infrared absorbing dye and has a very small incident angle dependence of transmittance so as to eliminate the change, to thereby suppress the dependence of the incident angle of light (refer to Patent Reference 1 (JP-A 2013-190553), Patent Reference 2 (JP-A 2014-052482), Patent Reference 3 (International Publication WO2014/002864), and the like, for example).
However, as an angle of incident light increases, there is generated a difference in optical characteristics of the dielectric multilayered film depending also on polarization components. Specifically, spectral transmittance curves of an s polarization component and a p polarization component become different. The above-described Patent References indicate a spectral transmittance curve with respect to obliquely incident (30°, for example) light, and discloses that a difference between the spectral transmittance curve and a spectral transmittance curve with respect to vertically incident (0°) light becomes small, but, there is no concrete description regarding polarization components. Further, when attention is focused on a particular polarization component (the s polarization component or the p polarization component), in a conventional optical filter, a shift amount becomes large, and a shift in a spectral transmittance curve in oblique incidence caused by the polarization component of incident light was not sufficiently eliminated. The shift (amount) mentioned here corresponds to a change (amount) of wavelength observed at a rising or a fall of transmittance in the spectral transmittance curve, in particular.
For this reason, the conventional optical filter has a problem that the incident angle dependence caused by the polarization components is generated. In particular, if incident angle dependence of light and polarization dependence in the optical filter increase in a region, in the vicinity of 700 nm being a boundary between a visible region and a near-infrared region, in which transition from transmission to cut-off occurs, the optical filter cannot obtain high-precision color reproducibility in a solid-state image sensing device. Further, if the transmittance of the optical filter increases due to the polarization dependence in the vicinity of 1150 nm, which is the longest wavelength of sensitivity of the solid-state image sensing device, the solid-state image sensing device senses an amount of light (noise) at a wavelength which should not be sensed, under normal conditions, by the solid-state image sensing device, resulting in that the high-precision color reproducibility cannot be obtained.